1. Field of the Invention
This invention relates to an anode component for primary, mechanically rechargeable metal-air batteries and, more particularly, to a reactive metal anode protected from corrosion by a hydrogel/inert polymer matrix, a method of manufacturing a reactive metal anode, a primary metal-air battery containing a reactive metal anode, and lightweight portable primary battery components that can be assembled in sitū.
2. Description of the Prior Art
Batteries having a metal anode and gas-diffusion cathode are generally known as metal-air batteries. Metal-air batteries have a high energy and power density, a flat discharge voltage, long storage life and use oxygen as the cathode. Air as the source of oxygen is inexhaustible. A metal-air battery can be used in field situations for portable radios, computers and/or the like.
During operation of this type of battery, oxygen from ambient air is electrochemically converted at a cathode to hydroxide anions and a metal anode is oxidized to metal cations. A suitable electrolyte, such as, an aqueous solution of an alkali or a neutral salt, KOH/NaOH and NaCl/KCl, respectively, electrochemically couples the anode and cathode to produce an electrical potential such that a current can flow to an external electrical load.
During the electrochemical reaction, a reactive metal anode, e.g., an aluminum anode, in each cell is consumed and oxygen from the atmospheric air is catalytically reduced and combined with water from the electrolyte forming hydroxyl (OH−) ions. Water is depleted via chemical reaction and the molar content of the electrolyte changes. The reactive metal anode can be reduced in thickness as it gives up its stored energy. In addition, the reactive metal anode can dissolve in the electrolyte. If the anode constitutes the only means for carrying current, the conductive capacity of the cell decreases over time as the anode is consumed. After the anode is expended to the point where it must be replaced, the cell must be refueled with a new anode and fresh electrolyte.
The prior art field batteries were usually a Li/thionyl chloride battery. They have an energy capacity in the range of 250–500 watt-hrs/kg. These batteries cannot be safely disposed in the environment and can pose an explosion hazard under certain conditions. In addition, these batteries are expensive and heavy.
Aluminum as the reactive metal would be desirable as an anode in a primary metal-air battery as it has high ampere-hour capacity, voltage, and specific energy and density. Aluminum is also inexpensive, abundant and lightweight. The major problem in using aluminum as the anode is the corrosion that eventually results in the destruction of the anode. It would be desirable to prevent the corrosion and thus slow the destruction of the anode. It would also be desirable to be able to immediately replace the anode, i.e., mechanically recharge the anode, once destroyed with another anode that is lightweight, portable and can continue to provide high power and energy density in the field. It would be desirable to use an alkaline electrolyte as it has higher conductivity than a neutral salt electrolyte and if the anode were aluminum, Al(OH)3 would dissolve in the alkaline electrolyte. Although it might also be desirable to use a neutral electrolyte as it is not corrosive to an aluminum anode and has fewer hazards. It would be desirable to have a lightweight, long lasting, portable, environmentally friendly, inexpensive aluminum anode component for insertion into a lightweight, portable, environmentally friendly, primary metal-air battery for immediate use as a source of high power to thereby prevent the loss of deliverable capacity and operational time. It would be desirable to be able to provide a lightweight, portable, environmentally friendly group of components for assembling a metal-air battery in sitū when needed, e.g., for use in portable radios and computers in the field. Finally, it would be desirable to be able to clean out the electrolyte chamber of any dissolved or undissolved reaction products using locally available water.